Modbus And Model 3711 Points - Emerson Micro Motion 3711 Configuration And Use Manual

Modbus Interface
In both modes, a Modbus message is placed by the transmitting device into a frame that has a known
beginning and ending point. ASCII and RTU modes use different frame structures. However, both
frame types contain the following:
• An address field, which identifies:
- Query frame – the Model 3711 unit to which the message will be transmitted
- Response frame – the host to which the reply will be returned
• A function field, which specifies:
- Query frame – the Modbus function to be performed by the Model 3711
- Response frame – the Modbus function performed by the Model 3711, or an error bit
• A data field, which supplies data required by the specified function:
- Query frame – the data field may contain the address of the start register, data to be written
to the Model 3711, and so on
- Response frame – the data field contains either data collected by the Model 3711 or an
exception response
The Model 3711 supports the following Modbus functions: 01, 02, 03, 04, 05, 06, 15, and 16.
During Model 3711 processing, datatype conversions are performed.
• Integer scaling may or may not be applied. Refer to Section 12.5.1 for a definition of integer
scaling, and to Section 12.5, Steps 4, 6, and 9 for your integer scaling configuration.
• Float scaling may or may not be applied. Refer to Section 12.5.1 for a definition of float
scaling, and to Section 12.5, Steps 4, 6, and 9 for your float scaling configuration.
• The configured datatype conversions are always applied. See Section 12.5.2.
Note: It is possible to configure datatype conversions for "no conversion."
Refer to standard Modbus documentation for detailed information on Modbus programming.
12.4

Modbus and Model 3711 points

Modbus programs may read and write to several different point types in Model 3711 memory. Access
to memory is performed through two different types of Modbus register, as shown in Figure 12-1:
• Modbus registers are used in ranges. Each Modbus register range references a Model 3711
point range, excluding history points. During configuration of Modbus registers, any required
datatype conversions may be specified.
• Modbus history access registers are also used in ranges, as pointers to ranges of history points.
Also as shown in Figure 12-1, the Events/Alarms index is used as a pointer to unacknowledged event
and alarm records.
Configuration of Modbus registers and Modbus history access registers is described later in this
chapter. The Events/Alarms index is configured on the Modbus History Access Registers panel.
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Micro Motion Model 3711 Gas Flow Computers